Challenges and Opportunities for Enhancing Sustainable ... - IITA

Cowpea genetics and breeding
the regular crop season (July–October) when day temperatures are below 35 o C and night
temperatures below 24 o C. In contrast to the heat susceptible lines, the heat tolerant lines
had normal pollen, good pod set, and normal grain yield. The best heat tolerant lines were
IT97K-472-12, IT97K-472-25, IT97K-819-43, and IT97K-499-38.
The details of work on chilling tolerance are reviewed in this volume by Hall et al. A
dehydrin gene involved in chilling tolerance during seedling stage has been identified (Ismail
et al. 1997, 1999) and mapped using recombinant inbred lines (Menendez et al. 1997).
The role of the dehydrin in chilling tolerance has been confirmed using near-isogenic lines
(Ismail et al. 2000) and efforts are underway to understand the mechanism involved in the
control of its expression.
Enhanced N-fixation and efficient use of phosphorus
Significant variation in cowpea rhizobium strains has been observed for nodulation in
cowpea (Mandal et al. 1999) but the local rhizobia invariably outpopulate the introduced
strains. Therefore, in recent years, major efforts have concentrated on exploiting genetic
variability in cowpea as a host for effective nodulation and nitrogen fixation (Buttery et al.
1992). Graham and Scott (1983) observed major genetic differences for nodulation and dry
matter and N accumulation among 12 cowpea varieties. They also observed a significant
relationship between total N and seed yield and nodule weight. Mandal et al. (1999) also
observed significant varietal differences in cowpea for nodule number and nodule weight as
well as for nitrogenase activity indicating a good possibility of breeding improved cowpea
varieties with enhanced N-fixation. Sanginga et al. (2000) screened 94 cowpea lines and
observed major varietal differences in cowpea for growth, nodulation, and arbuscular mycorrhizal
fungi root infection as well as for performance under low and high phosphorus. The
improved cowpea variety IT86D-715 showed equally good growth under low as well as high
phosphorus levels. It also showed better N-fixation than others. Based on its adaptability to
grow in low P soils and overall positive N balance, they recommended cultivation of IT86D-
715 cowpea variety in soils with low fertility. Kolawale et al. (2000) screened 15 cowpea
varieties for tolerance to aluminum and to determine the effect of phosphorus addition on
the performance of Al-tolerant lines. The results indicated IT91K-93-10, IT93K-2046-1, and
IT90K-277-2 cowpea varieties to be tolerant to aluminum and they gave a higher response
to phosphorus fertilization when grown in soils with aluminum toxicity problems. Singh
et al. (1998) evaluated improved cowpea varieties under low and high fertility and they
also observed major varietal differences. They found IT96D-772, IT96D-739, IT96D-740,
and IT96D-666 cowpea varieties to be good performers under low as well as high fertility
whereas most other varieties were poor in poor fertility and good in good fertility. These
studies further indicate a good possibility of developing improved cowpea varieties with
enhanced nitrogen fixation and higher yields under low phosphorus as well as in soils
with aluminum toxicity. There is a need for closer interactions between cowpea breeders
and soil scientists and soil microbiologists.
Improved nutritional quality
Cowpea is a major source of protein, minerals, and vitamins in the daily diets of the rural
and urban masses in the tropics, particularly in West and Central Africa where it complements
well with the starchy food prepared from cassava, maize, millet, sorghum, and
yam. Systematic efforts have just begun at IITA and a few other institutions to develop
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